In one conventional type of a laser printer, a developing unit is provided detachably from a main frame. In such laser printer the developing unit has already been assembled to the main frame to reduce a packaging size for the purpose of transportation. However, with such assembled state, a developing roller of the developing unit is in contact with a photosensitive drum provided in the main frame. As a result, a surface of the photosensitive drum is damaged due to frictional contact with the developing roller if vibration is imparted on the laser printer during transportation.
Japanese Patent Application Publication No. 2006-330481 discloses a laser printer for protecting the photosensitive drum from damage against a charging roller during transportation. To this effect, a spacer member is provided to position the charging roller away from the photosensitive drum. More specifically, the charging roller is urged toward the photosensitive drum by an urging force of a spring. The charging roller has a bearing member formed with an engagement recess with which the spacer member is to be engaged. If the spacer member is engaged with the recess, the bearing member is moved away from the photosensitive drum along with the charging roller against the urging force of the spring. Thus, the charging roller can be spaced away from the photosensitive drum.